A solar cell with a property of semiconductor converts a light energy into an electric energy.
A structure and principle of the solar cell according to the related art will be briefly explained as follows. The solar cell is formed in a PN-junction structure where a positive(P)-type semiconductor makes a junction with a negative(N)-type semiconductor. When a solar ray is incident on the solar cell with the PN-junction structure, holes(+) and electrons(−) are generated in the semiconductor owing to the energy of the solar ray. By an electric field generated in an PN-junction area, the holes(+) are drifted toward the P-type semiconductor, and the electrons(−) are drifted toward the N-type semiconductor, whereby an electric power is produced with an occurrence of electric potential.
The solar cell can be largely classified into a wafer type solar cell and a thin film type solar cell.
The wafer type solar cell uses a wafer made of a semiconductor material such as silicon. In the meantime, the thin film type solar cell is manufactured by forming a semiconductor in type of a thin film on a glass substrate.
With respect to efficiency, the wafer type solar cell is better than the thin film type solar cell. However, in the case of the wafer type solar cell, it is difficult to realize a small thickness due to difficulty in performance of the manufacturing process. In addition, the wafer type solar cell uses a high-priced semiconductor substrate, whereby its manufacturing cost is increased.
Even though the thin film type solar cell is inferior in efficiency to the wafer type solar cell, the thin film type solar cell has advantages such as realization of thin profile and use of low-priced material. Accordingly, the thin film type solar cell is suitable for a mass production.
The thin film type solar cell is manufactured by sequential steps of forming a front electrode on a glass substrate, forming a semiconductor layer on the front electrode, and forming a rear electrode on the semiconductor layer.
Hereinafter, a related art thin film type solar cell will be explained with reference to the accompanying drawings.
FIG. 1 is a cross section view illustrating a related art thin film type solar cell.
As shown in FIG. 1, the related art thin film type solar cell includes a substrate 10, a front electrode 20 on the substrate 10, a semiconductor layer 30 on the front electrode 20, and a rear electrode 50 on the semiconductor layer 30.
The front electrode 20 forms a positive(+) electrode of the thin film type solar cell. Also, the front electrode 20 is made of a transparent conductive material since the front electrode 20 corresponds to a solar ray incidence face.
The semiconductor layer 30 is made of a semiconductor material, for example, silicon. The semiconductor layer 30 is formed in a PIN structure with a P(positive)-type silicon layer, an I(intrinsic)-type silicon layer, and an N(negative)-type silicon layer deposited in sequence.
The rear electrode 50 forms a negative(−) electrode of the thin film type solar cell. The rear electrode 50 is made of a conductive metal material, for example, aluminum.
Generally, the related art thin film type solar cell uses the substrate 10 made of glass. However, if manufacturing the thin film type solar cell with the glass substrate 100, a direction of solar ray incident on the substrate 10 is not very different from a direction of solar ray entering the front electrode 20 through the substrate 10. Thus, it is difficult to improve the efficiency of solar cell due to the limit in collection of the solar ray.